Skin deep oxide

["Finn Hammer" <f-hammer-at-post5.tele.dk> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

All!

It has been mentioned some times that alluminium is a poor conductor at
high frequencies. Also that the oxide layer of same is thick. I disagree
with the last statement, the oxide layer of alluminium is very thin, and
should not be confused with the glass layer known as anodizing.

But what if this oxide layer is a poor conductor of rf, then so is the
enamel layer of copper magnet wire, and this layer certainly never kept
us from using the wire to wind secondary`s.

What I`m trying to say, I think, is: how _bad_ a conductor must a given
coating, be it varnish or oxide, be, before we can assume that the
current stays out of it, so that it can be neglected, like we surely do
in case of it being varnish, on the other hand,  when it is oxide, we
worry.

Won`t the current just avoid the oxide layer as it would enamel, and
sink a bit deeper _in_.

Cheers, Finn Hammer

aka:  hammer-at-wimshurst-dot-com